996TT Brake Caliper Piston sizes

[spuggy]

I've been searching all over for some time, but can't seem to find the sizes of the pistons fitted to the 996TT calipers.

Does anyone know?

I'd like to pull the trigger on a brake upgrade. I'm concerned the 996TT setup might be more front-biased than I'd prefer - but I don't have much confidence in the piston sizes (36/44 front, 28/30 rear) I think I found for these brakes.


Thanks for any help!

[Bill Verburg]

Originally Posted by spuggy

I've been searching all over for some time, but can't seem to find the sizes of the pistons fitted to the 996TT calipers.

Does anyone know?

I'd like to pull the trigger on a brake upgrade. I'm concerned the 996TT setup might be more front-biased than I'd prefer - but I don't have much confidence in the piston sizes (36/44 front, 28/30 rear) I think I found for these brakes.


Thanks for any help!

36/44front 28/30 rear, yes they are very front biased

[911st]

If I may tag along.

I would also like to know the rear 3.2 Carrera piston size?

Also, is it better if one has the choice to make the car a bit rear biased and add an adjustable Tilton valve on it, or to get close without any valve if that is the only two choices?

[Bill Verburg]

Originally Posted by 911st

If I may tag along.

I would also like to know the rear 3.2 Carrera piston size?

Also, is it better if one has the choice to make the car a bit rear biased and add an adjustable Tilton valve on it, or to get close without any valve if that is the only two choices?

'84-89 3.2 Carrera rear is 42mm x2

I like as much rear bias as you can get away w/, you want to relieve the front of as much load as much as is practical. To do this you want an effective lsd and stiffish suspension. The 3.2s unfortunately have a tad too much rear. An adjustable valve like the click stop Tilton is an acceptable tuning tool. Better of course is a twin master setup w/ adjustable bar and/or staggard m/c pistons. and even better is good native bias.

[spuggy]

Originally Posted by Bill Verburg

36/44front 28/30 rear, yes they are very front biased

Excellent, many thanks Bill!

Looks like I'll be going for regular 996 stuff then, as the bias is much closer to ideal @ 1.7.

Originally Posted by 911st

I would also like to know the rear 3.2 Carrera piston size?

3.2 has a single pair of 48mm front pistons, single pair of 42mm rear pistons for a uncorrected (no bias valve) F/R bias ratio of 1.3.

[Bill Verburg]

Originally Posted by spuggy

Excellent, many thanks Bill!

Looks like I'll be going for regular 996 stuff then, as the bias is much closer to ideal @ 1.7.




3.2 has a single pair of 48mm front pistons, single pair of 42mm rear pistons for a uncorrected (no bias valve) F/R bias ratio of 1.3.

Yep, 996 is 36/40 w/ 28/30 rear for 1.72 f/r ratio, rotor diameters will also affect total bias as will differential pad materials.

There is no 1 ideal, I'm pretty comfortable w/ ~1.5 to ~1.8 depending on other factors like lsd, wheels, tires, suspension etc. most 911s have always been ~1.6 going to ~1.5 on some RSRs and RS's

[911st]

How much dose pad size effect the ideal ratio?

That is, if some one put say Wilwood calipers in the front w a pad that is about 5+ sq inch's w the small pad Carrera rears calipers?

Thx.

[spuggy]

Originally Posted by 911st

How much dose pad size effect the ideal ratio?

Pad area is a factor in thermal transfer/capacity, but not clamping force - if piston sizes are the same, the same clamping force is transmitted to the pad.

With a larger pad, the pressure per unit area (e.g. lbs/sq in) is lower on the larger pad area, but the total pressure is the same for both pads.

Pad friction material composition and rotor diameter can both change the effective ratio, but pad area doesn't.

[911st]

Interesting?

Then a larger pad must not get as hot?

Thx

[spuggy]

Originally Posted by Bill Verburg

rotor diameters will also affect total bias as will differential pad materials.

Hmm. Taking rotor diameters into account and calculating torque based on the mid-point of the (guessed) swept height of the pad skews the figures about 15%. Of course, in the "wrong" direction...

Would you have any measurements for 996 and/or 996TT pads? Actual height of the friction material would be perfect, but I can probably extrapolate from the backing plate sizes...

[Flieger]

Originally Posted by 911st

Interesting?

Then a larger pad must not get as hot?

Thx

Friction force= mu * total applied force

mu= coefficient of friction, dependent on material properties of the surface.

applied force= pressure * area = how forceful your leg can push the pedal.

[Bill Verburg]

As Spuggy said, pad area has no effect on brake torque. The large pads just spread the forces and heat over a larger area so that they will last longer.

As to the radius of the swept area for 996, no I've never worked through that particlular setup, if you use roughly the same radius rotors front and rear you will be good. I believe from memeory that stock is 330mm f/r